Sustained improvement in Expanded Disability Status Scale as a new efficacy measure of neurological change in multiple sclerosis: treatment effects with natalizumab in patients with relapsing multiple sclerosis

Background: Validated measures of sustained improvements in neurological function have not been established for multiple sclerosis (MS) clinical studies. Objective: To evaluate sustained Expanded Disability Status Scale (EDSS) change as a potential indicator of neurological improvement and as an outcome measure in MS clinical studies. Methods: Analyses were performed on patients (n = 620) from the pivotal natalizumab study AFFIRM with baseline EDSS scores >= 2.0. Cumulative probabilities of neurological improvement, defined as a 1.0-point decrease in EDSS score sustained for >= 12 weeks, were estimated by Kaplan-Meier analysis. A Cox proportional hazards model identified associated baseline factors and examined treatment effects. Results: Sustained improvement (as well as sustained worsening) in neurological disability was seen in AFFIRM patients. Sustained EDSS changes correlated well with quality of life measurements (SF36 and VAS). Natalizumab increased the cumulative probability of improvement over 2 years by 69% versus placebo (HR = 1.69; 95% CI 1.16-2.45; p = 0.006). Sensitivity analyses showed consistent benefits of natalizumab with variations in improvement magnitude and duration, and baseline disease activity. Conclusion: These analyses demonstrate that sustained EDSS improvement is an additional measure that is sensitive to treatment effects over 2 years and correlates with quality of life. Further research is warranted to validate its use as an MS study clinical outcome.